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Model34904
s. Set
RATIO
switch
to
EXT
REF
I V'
Adjust
efgni
(Bias. Atlj.)
with
both
positive and
negative
10.0000
V
inputs
for
display
of
zero
t 0'0005
V'
h.
Repeat
steps
a
through
g
until
all readings
are
colTect.
i.
Disconnect
lMft
resistor
from
EXT
REF
termi
nals.
Set
RATIO
switch
to
INT
REF,
FUNCTION
to
DC,
RANGE
ttr
10
V.
i. Connect
a
mercury
battery
between
9'5
V and
10.5
V.
or
other
floating
voltage
source
stable
within
1 mV/hr,
to
INPUT
terminals,
-
to
Higfr,
+
to
Low'
Note
3490A
reading.
k.
Connect
dc
standard
to
EXT
REF
terminals and
set standard
output
to
positive
voltage
equal
to negative
reading
in
steP
j.
l. Set
RATIO
switch
to EXT
REF
l0 V-
Note 3490A
display.
m. Reverse
the polarity
of the
voltage
at both the
INPUT
and
the
EXT REF
terminals.
Adjust
Al3Rl7,
repeating steps
k through m until the
readingin step
I is
equal to the
reading in step
m.
(Polarity
should
be
-
for
both
readings.)
n.
Reduce
EXT
REF voltage to
l/10
the voltage
selected
in step
k.
S€t RATIO switch
to
EXT REF I
V.
With
mercury
battery
connected to
INPUT,
-
to
HIGH,
+
to
LOW, note
3940A
display.
o.
Reverse
the polarity
of the
voltage
at both the
INPUT
and the
EXT
REF terminals.
Adjust
Al3R8,
repeating steps
n
and o until
the
reading in
step o is
equal to
the
reading
in step
n.
@olarity
should
be
-
for
both
readings.)
p.
Repeat
steps
j
through
o
until
all readings
are
correct.
q.
Connect
mercury
battery
to
IMUT terminals,
-
to
HIGH,
+
to
LOW.
r. Connect
dc standard
to
EXT
REF terminals
and
set
standard
output
to positive
voltage
equal to
negative
reading in
step
j.
ADJUSTMENT PROCEDURES
Section
V
s.
Set
RATIO
switch to EXT REF lOV.
Adjust
Al3Rl4
(10
V Adj) for display
of
-
10.0000.
t. Reduce EXT
REF
voltage
to
l/10 the
voltage
selected
in step
k
(positive).
Set
RATIO
switch to
EXT
REF I
V. Adjust Al3Rl2
(lV
Adj) for
display
of
-
10.0000.
u. Set RATIO switch to INT
REF, FUNCTION
to
TEST,
RANGE to 3.
This test alternates
positive
and
negative
readings.
Ifthe
readings are not equal t
I count
and between
!
0.99992 and
!
0.99999,
adjust
AlAlR3lT
C
Refl
to
obtain this condition.
Record
both
readings
(after
adjustment).
v. Set RATIO
switch to EXT REF l0V.
Apply
-
10.0000
V
to
EXT REF terminals.
Readings
will
alternate
+
and
-
as
in
previous
step.
Record
positive
reading.
w. Adjust A13Rl9
(Offset
301)
for
positive
display"
equal
to
(positive
reading,
step
u)
+
(positive
reading,
step
v)
L
x.
Adjust
AlAlR3lT for
positive
display
equal
to
positive
reading
in
step u.
y.
Positive and
negative displays
should
now
be
equal
t I count, and
equal
to readings
recorded
in
step n
+
I
count, respectively.
If not,
repeat
this adjustment
procedure
(steps
a
through x).
z.
Perform DC Amplifier
Adjustment,
Paragraph
s-59.
NOTE
In
order
to
operate
the
3490A with
the
Ratio
Assembly
A
I 3
removed and the Ratio
Jumper
Assembly
A26 inserted
in
its
place,
it
will be necessary
to
perform
the
Reference
Adiustmen
t s, Paragraph
5-5 7.
5-19